Blending of two or more polymers is a common practice, the objective being to produce a composition having improved mechanical, rheological, and/or degradative properties compared to the individual polymers. Blending can be an effective way to customize a composition, providing properties which may not be available in a single known polymer, or which would require the time-consuming and expensive development of a new polymer.
A virtually infinite number of polymer blends is theoretically possible, but not all polymer blends result in compositions with desirable properties. If the component polymers are incompatible, the resulting blend often has inferior properties. This can especially be the case for blends involving fluoropolymers. Generally, incompatibility is the rule, and compatibility is the exception.
Compatability is often established by the observation of mechanical integrity under the intended conditions of use of a composite or an immiscible polymer blend. Compatibilizers, which are usually block or graft copolymers having segments in common with the main polymer components of the two polymers being blended, can be used to improve the chances of obtaining a compatible blend. But even the use of a compatibilizer does not assure success. Most examples of successful use of compatibilizers involve polyolefin blends.
Fluoroplastics are unique among polymers, offering performance characteristics unobtainable with most other polymers. Some commercially available fluoropolymers include polytetrafluoroethylene (PTFE), fluorinated ethylene-propylene copolymer (FEP), perfluoroalkoxy resin (PFA), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), ethylene-tetrafluoroethylene copolymer (ETFE), polyvinylidene fluoride (PVDF), and polyvinylfluoride (PVF), among others. Some fluoroplastics such as PTFE are completely fluorinated, while others such as ETFE or PVDF are only partially fluorinated. Typically, fluoroplastics are characterized by high melting points and low glass transition temperatures, enabling them to be advantageously used over a wide temperature range, such as from well below 0° C. to +260° C. Other desirable properties of fluoroplastics include their excellent solvent resistance, electrical insulative properties, low coefficient of friction, low flammability, low gas permeability, and high inertness and stability. The selection of commercially available fluoroplastics is typically more limited than for non-fluorinated polymers, because options regarding both the choice of fluorinated monomer and type of polymerization chemistry are much more limited. Thus, it is desirable to develop novel blends of fluoroplastics having improved properties.
It is known that the incorporation of nanocomposite additives into fluoroelastomeric compositions can improve some properties of the compositions, particularly combustion properties including non-dripping characteristics. Known nanocomposites that are suitable for incorporation into these compositions are preferably by montmorillonites (the main fraction of the clay mineral bentonite), which are layered alumino-silicate or magnesium-silicate materials whose individual platelets measure on the order of one micron diameter, giving them an aspect ratio of about 1000:1. It is this morphology that leads to increased barrier properties to moisture, resistance of the composition to deformation, resistance to whitening or blooming, improved mechanical strength, sizeable drop in heat release rate and smoke properties, improved flame retardancy and char integrity of the polymer compositions. The nanocomposite additives can be chemically modified to increase the hydrophobicity of their surfaces, thereby enhancing their fire performance effectiveness.
It is also known that blending or alloying fluoroelastomeric compositions with suitable olefinic or polyvinylchloride (PVC) polymers improves the flexibility, electrical properties, and manufacturing costs of the resulting blend or alloy. Suitable polymers to make the blends and alloys of these compositions include: polytetrafluoroethylene (PTFE) fluorocarbons, fluorinated ethylene/propylene (FEP) fluorocarbons, perfluoroalkoxy (PFA) fluorocarbons, ethylene tetrafluoroethylene (ETFE) fluoropolymers, polyvinylidene (PVDF) fluoropolymers, ethylene chlorotrifluoroethylene (ECTFE) fluoropolymers, fluoro-chlorinated homopolymers, copolymers and terpolymers, very low density polyethylene (VLDPE), low density polyethylene (LDPE), linear low density polyethylene (LLDPE), high density polyethylene (HDPE), polypropylene (PP), ethylene propylene copolymer or rubber (EPR), ethyl vinyl acetate (EVA), ethylene ethyl acrylate (EEA), ethylene methyl acrylate (EMA), ethylene butyl acrylate (EBA), and ethylene-based homopolymers, copolymers and terpolymers, and PVC-based homopolymers, copolymers and terpolymers.
Ebrahimian, et al, U.S. Pat. No. 6,797,760, discloses a non-dripping, flame retardant, fluoropolymeric insulative composition that comprises: (a) a fluoropolymeric base polymer; and (b) a nanoclay additive. The preferred nanoclay additive is selected from the group consisting of synthetic silicate montmorillonites, natural layered silicate montmorillonites and a layered alumna-silicate. Such compositions are especially useful for coating wires and conductors employed in high-speed telecommunication data transmission cables. A method for preparing an exfoliated thermoplastic elastomer blend of a fluoropolymer and a nanocomposite comprising dynamically mixing said fluoropolymer and said nanocomposite in a ratio of from about 99:1 to about 50:50 parts by weight, respectively. While the previous compositions were suitable for plenum rated fiber optic cable they are unsuitable for limited combustible applications because of their high heat of combustion values.
Known prior art fluoropolymer compositions have been filled to about 20%- about 60% by weight. There is a need for continued development in the field to produce alternative compositions with desired function specific characteristics at lower costs.